Insulating composition.



UNITED stra'rrusfrann'r orric.

LAWRENCE E. BARRINGEB, OF SCHEN'EGTADY, NEW YORK, ASSIGNOR T0! GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

INSULATING: COMPOSITION.

1,091,725. No Drawing.

To all whom it may concern:

Be it known tiat I, LAWRENCE E. BAP.- RINcnR, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements .in Insulating Compositions, of which the following is a specification.

The present invention comprises a composition suitable particularly for insulating electrical apparatus, such as transformers or generators and the like. Insulation of this character must not only be cheap, permanent, have high dielectric properties an insoluble in the mineral oils used for cooling electrical apparatus, but must also havehysical properties enabling it to be read- 11y applied and retained by the coils or other objects to be impregnated. Forexample, it should be solid at operating temperatures, but fusible at a temperature attainable for impregnating the apparatus. Some fusible insulatin compounds are more or less soluble in oiTs or have too high a flow point; others have a flow point which becomes pro gressively higher in the impregnating tank and finally the bath becomes unfit for further use by becoming too viscous.

I have found a mixture comprising gum copaL eastor oil and the resin extracted by solvents from crude rubber, and known as rubber resin to meet all the above requirements.

Although a mixture of gum copal and castor oil has insulating properties and is insoluble in mineral il, the flow point of the mixture'o'f these substances when heated to about 150 deg. C. soon begins to ascend very rapidly, and within a veryfew days the mixture turns into a rubbery mass which cannot be liquefied by beating. In this condition the mixture, of course, isuntitted for the purpose of impregnation. -When rubbe'r resin is added to gum copal and castor oil, the composition will remain liquid at 150 deg. C. for two or three weeks 01' even longer. The flow point rises somewhat, butnot to such Specification of Letters Patent. Application filed January 18, 1913.

Patented Mar. 3i, 1914.. Serial no. 742,971.

an extent as to cause the dii'iiculty pointed out above. This mixture is, therefore, especially suitable for use in impregnating tanks where continuous liquidity is desirable to impregnate electrical coils, or the like.

I prefer to use a mixture in the following proportions Rubber resin Sparts. Castor oil 10 Gum copal 82 These proportions need not be strictly adhered to, but when the proportion of castor oil is varied, it chan es the lnitial fiow point of the material. I hen the proportion of castor oil is decreased the dew point will gradually rise and conversely the increase of cast-or oil content will lower the fiow point. \V hen it is desired that the initial flow point be above 100 deg. (1., the castor oil should not be less than 5% and not over 15%. The proportion of rubber resin may be varied from about 5% to 20% and the proportion of gum eopal fromabout to 85%, depcnding somewhat on the proportion of the other ingredients. The mixture is insoluble in mineral oils, such as transil oil, is very adhesive and has very high insulating properties.

In some cases the rubber resin may be replaced in part by ordinary resin, or colophony, with a. consequent eheapening of the COIUPOSiilOIi, but I find that when rubber resin alone is used as a flux the compound clings better to the fabric insulation of the coils.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A composition of matter comprising copal, castor oil, and rubber resin.

2. An insulating composition comprising by weight about 70 to parts of copal, 5 to 15 parts of Castor oil, and 5 to 20 parts of rubber resin. i

3. A filler for oil immersed electrical coils comprising substantially by weight 82 parts gum eopal, 10 parts, caster oil and 8 parts from crude zrubber, charlsuluting properties, con- ,firiiditj' when heziied and insnlucmuposition consisting of my 011 rubber z'esln and (2010- In Witness whereof, I have hereunbe set my hand this 17 th day of January, 1913.

LAWRENCE E. BARRINGER.

Witnesses BENJAMIN HULL, HELEN ORFORD. 

